1. Field of the Invention
The invention relates, generally, to pneumatic valve assemblies and, more specifically, to a directly operated pneumatic valve having an air assist return.
2. Description of the Related Art
Directly operated, or actuated, pneumatic valves are well known in the art for controlling the flow of pressurized air therethrough. Directly operated valves may be used alone or in connection with, for example, spool valves and regulators that, in turn, control the flow of pressurized air to and from various pneumatically actuated devices such as press clutches, air brakes, air cylinders or any other pneumatic device or application requiring precise control of operating air. More specifically, two-way, three-way and four-way direct operated valve assemblies are commonly employed in these environments. Such valves typically include a valve body having a valve bore formed in the valve body. A valve member is movably supported within the valve bore from one position to another in direct response to an operative force placed on the valve member by an actuator. A plurality of ports are used to connect the valve assembly to a system supply pressure as well as the various active devices that the valve may control. The actuator is typically an electromagnetically operated solenoid that is energized to move the valve member to a predetermined position within the valve bore. A return spring is often employed to bias the valve member back to a known non-energized position. Valves of this type are employed in a wide variety of manufacturing environments where a high flow rate and very fast response time are desired.
As the technology for these valves has advanced, there has been an increase in the demand for smaller valves that are designed to be employed in operating environments with ever decreasing physical dimensions. In addition, the advance in technology has dictated that the valves must be able to operate with very fast cycle times. In fact, the demand for greater speed and shorter response time is an ongoing requirement for valves of this type. However, in the past, certain design barriers have limited the extent to which the size of the valve assembly could be reduced while at the same time increasing its speed. When the valve member and the valve bore are reduced below a predetermined size, the return spring may be of insufficient physical size and mechanical strength to overcome the inertia of the valve member. In addition, after the valve member has been biased in one direction by the actuator, frictional forces and surface adhesion can build up at the interface of the valve member seals and the valve bore. These frictional forces and related surface adhesion can act to inhibit movement of the valve member in the opposite direction and reduce valve speed and therefore increase valve response time. In this case, the return spring may be unable to provide enough biasing force to quickly or effectively move the valve member from its energized position and return it to the non-energized position when the actuator force is removed. When this occurs, accurate control of the active device is lost. To counter this shortcoming, various design strategies have emerged. However, the design strategies that have been proposed in the related art all suffer from the disadvantage that they add supplemental mechanisms, hardware, or require a remote mounting of the valve.
For example, one design strategy proposed in the related art involves the use of dual electromagnetic actuators to move the valve member in opposite directions. Thus, the return spring is replaced by an electromagnetic actuator such as a solenoid. Unfortunately, this solution adds the complexity of a second solenoid and its associated parts, and also creates another size limiting boundary. On the other hand, single electromagnetic actuators that energize in both directions have been suggested in the related art. However, these single electromagnetic actuators require a bulkier double wound actuator as well as additional electronic circuitry and controls. Thus, directly operated valves that employ the bulkier single electromagnetic operators are typically mounted in a remote location relative to the pneumatically actuated device they control. Unfortunately, the remotely located valves defeat the purpose of smaller, lighter, and more accurate valve designs that can be mounted in very close proximity to the active devices. Also, they must be interconnected via conduits or other flow passages, which require additional hardware and plumbing, and can lower pneumatic efficiencies and introduce line losses within the system.
While the use of the larger conventional valves, either remotely disposed or with the addition of other components, has generally worked for their intended purposes, there remains an ongoing need in the art to simplify pneumatic systems and thereby lower costs of manufacture and/or assembly by creating ever smaller, yet highly accurate, fast actuating, directly operated pneumatic valves. Smaller directly operated valves can be located in very close proximity to active system components, thereby shortening flow paths, reducing or eliminating additional plumbing and hardware, and increasing pneumatic flow efficiency. Unfortunately, the design strategies that have been proposed in the related art have failed to overcome the problems created when the valve member and bore are reduced in size past the point where a return spring has the physical size and mechanical force to quickly, effectively, and repeatedly return the valve member of a fast acting valve to the non-energized position.
The present invention overcomes these design barriers and other disadvantages of the related art in a directly operated valve assembly. More specifically, the present invention is directed toward a directly operated valve assembly including a valve body having a pressurized air supply inlet port in communication with a source of pressurized air, and at least one cylinder port. A valve bore extends axially within the valve body, and a valve member is moveably supported within the valve bore between predetermined positions to selectively direct pressurized air from the inlet port through the cylinder port. An actuator is mounted to the valve body for moving the valve member in a first direction and a biasing member is disposed between the valve member and the valve body to provide a biasing force to the valve member in an opposite direction. Also, an air-assist passage is included for providing a source of pneumatic pressure that acts in combination with the biasing member to operatively move the valve member in a direction opposite to the movement induced by the actuator.
The directly operated valve assembly of the present invention has distinct advantages over the valves known in the related art. The air-assist passage provides a source of pneumatic pressure from the pressurized cylinder port that acts in combination with the biasing member to operatively move the valve member in a direction opposite to the movement induced by the actuator. Importantly, the air assist facilitates a faster acting valve. More specifically, valve assemblies employing the air assist of the present invention may include a smaller biasing member that generates less force than would be required without the air assist. Because the biasing member generates less force, the actuator has less force to overcome and therefore moves the valve member to its first position faster. In addition, the biasing member, along with the air assist provided through the passage, will be able to quickly and efficiently move the valve member away from its second, or energized, position once the solenoid assembly is de-energized. The air-assist passage provides the necessary mechanical impetus to assist in moving the valve member to the de-energized position.
Thus, the directly operated valve assembly of the present invention overcomes the shortcoming and drawbacks of conventional valve assemblies when they are so reduced in size such that the biasing member alone is of insufficient physical size and mechanical strength to repeatedly, quickly, and efficiently overcome the inertia of the valve member and/or exceed the frictional adhesion forces acting at the valve bore. This allows a very fast acting valve assembly to be constructed in sizes below the conventional standards.